Semiconductor Diodes Fabricated by Aspect Ratio Trapping with Coalesced Films

ABSTRACT

A method of forming a photonic device that comprises a substrate and a dielectric material including two or more openings that expose a portion of the substrate, the two or more openings each having an aspect ratio of at least 1. A bottom diode material comprising a compound semiconductor material that is lattice mismatched to the substrate occupies the two or more openings and is coalesced above the two or more openings to form the bottom diode region. The method may further include forming a top diode material and an active diode region between the top and bottom diode materials.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/288,197, titled “Semiconductor Diodes Fabricated by Aspect RatioTrapping with Coalesced Films,” and filed May 27, 2014, whichapplication is a continuation, of U.S. patent application Ser. No.13/650,206, filed Oct. 12, 2012, titled “Semiconductor Diodes Fabricatedby Aspect Ratio Trapping with Coalesced Films,” now U.S. Pat. No.8,765,510 issued Jul. 1, 2014, which is a divisional of U.S. patentapplication Ser. No. 12/684,499, filed Jan. 8, 2010, now U.S. Pat. No.8,304,805 issued Nov. 6, 2012, titled “Semiconductor Diodes Fabricatedby Aspect Ratio Trapping with Coalesced Films,” which claims the benefitof U.S. Provisional Patent Application Ser. No. 61/143,602, filed onJan. 9, 2009, entitled “Semiconductor Diodes Fabricated by Aspect RatioTrapping with Coalesced Films,” which applications are herebyincorporated herein by reference in their entireties.

This application relates to the following co-pending and commonlyassigned patent application: TSM09-058US-AW, Ser. No. 12/684,797, filedon Jan. 8, 2010, entitled “Diode-Based Devices and Methods for Makingthe Same,” which application is hereby incorporated herein by reference.

U.S. patent application Ser. No. 12/100,131 filed on Apr. 9, 2008 claimspriority to U.S. Provisional Patent Application No. 60/922,533 filed onApr. 9, 2007, which are hereby incorporated by reference in theirentirety.

BACKGROUND

The present invention relates generally to semiconductor diodes madefrom compound semiconductors or other lattice-mismatched semiconductorson silicon wafers, as well as methods of fabricating such semiconductordiodes, and more particularly to photonic applications such as lightemitting diodes (LEDs), lasers, photovoltaics, and other optoelectronicuses.

This section provides background information and introduces informationrelated to various aspects of the disclosures that are described and/orclaimed below. These background statements are not admissions of priorart.

The majority of chip manufacturing takes advantage of silicon processingon high-quality, large-area, low-cost silicon wafers. Commercialmanufacturers of devices made from compound semiconductors such asgallium arsenide and indium phosphide generally have been unable to takeadvantage of silicon wafers. They typically build light emitting diodes(LEDs), multi-junction solar cells, and other compound semiconductordevices on small, expensive wafers made of materials such as sapphire,germanium, gallium arsenide, or silicon carbide.

The challenge of making compound semiconductor devices on inexpensivesubstrates has widespread economic implications. Compound semiconductorsare an important component of our communications infrastructure becausethey can emit and detect light. They are the materials in the lasersthat transmit signals through optical fibers, the sensors that receivethose signals, the amplifiers in cellular telephones, the amplifiers incell phone base stations, and the circuits that transmit and receivemicrowave signals.

Light-emitting diodes typically consist of gallium nitride filmsdeposited onto sapphire or silicon carbide wafers. These exoticsubstrates contribute to the high cost of LEDs. A sapphire wafer 4inches in diameter typically costs around $130, and a 2-inch siliconcarbide wafer can cost about $2000. By contrast, an 8-inch siliconwafer, which provides four times as much surface area as a 4-inch waferand 16 times as much surface area as a 2-inch wafer, typically costsless than $100.

High-efficiency multi-junction solar cells typically contain layers suchas germanium, gallium arsenide, and indium gallium phosphide depositedonto germanium wafers. As is the case with wafers for LEDs, germaniumwafers similarly are smaller and significantly more expensive thansilicon wafers.

The ability to create compound semiconductor devices on silicon waferswould facilitate market growth in several key industries.

Two key technical barriers have inhibited the practical fabrication ofcompound semiconductor devices on silicon wafers: the mismatch oflattice constants and the mismatch of thermal expansion coefficients.

Lattice Mismatch: In a crystal, the atoms sit in a regular periodicarray known as a lattice. The distance between the atoms, known as the“lattice constant,” is typically a few angstroms (1 ångstrom=10-10meter). Silicon has a smaller lattice constant than compoundsemiconductors. When compound semiconductors grow on silicon,crystalline imperfections known as misfit dislocations appear at theinterface. The misfit dislocations create other crystalline defectsknown as threading dislocations, which propagate upward from theinterface. Threading dislocations diminish the performance and thereliability of compound semiconductor devices such as lasers, solarcells, light-emitting diodes, etc.

Thermal Contraction Mismatch: Compound semiconductors typically grow athigh temperatures, which can exceed 1000° C. When the wafer cools, thecompound semiconductor film may contract more than the silicon wafer. Asa result, the wafer may bow in a concave manner, stressing andultimately cracking the film.

Until recently, the most promising previous efforts to grow high-qualitycompound semiconductors onto silicon substrates have relied on threeapproaches: graded buffer layers, wafer bonding, or selective growth onmesas. None of these approaches has achieved commercial success.

In graded buffer layers, the composition of the material changesgradually from substantially pure silicon to a compound semiconductor.Since the lattice constant also changes gradually, crystalline defectsare less likely to form at the interface. Unfortunately, the gradedbuffer layers have to be relatively thick (about ten microns for a 4%lattice mismatch). The thick buffer layer increases both the costs andthe likelihood of cracking.

Wafer bonding involves growing devices on expensive substrates, thenlifting off the devices and bonding them to a silicon wafer. Thisapproach rules out modern silicon processing as a route to costreduction. Furthermore, bonding typically requires temperatures above300° C. When the materials cool, the compound semiconductors may crackbecause they contract more than the silicon wafer.

Selective growth on a mesa exploits the mobility of some dislocations.The strategy is to deposit compound semiconductors in small regions (10to 100 microns in length), thereby providing a short path where mobiledislocations can glide to the edge of the region and remove themselvesfrom the device. However, structures created by this technique typicallyhave a high density of threading dislocations (more than 100 million persquare centimeter). This technique can't remove immobile dislocations,which predominate when the lattice mismatch exceeds 2%.

Aspect Ratio Trapping (J. S. Park et al., APL 90, 052113 (2007, herebyincorporated by reference) is a recently developed technology that makesit possible to deposit high-quality compound semiconductors, germaniumor other lattice-mismatched materials on silicon wafers. FIG. 1illustrates the principle of Aspect Ratio Trapping. We deposit a thinfilm of dielectric material (20) such as silicon dioxide (SiO2) orsilicon nitride (SiNx) onto a silicon wafer (10). Those of ordinaryskill in the art can select a variety of dielectric materials such asSiOxNy, and silicates or oxides of materials such as Hf or Zr.

We etch a trench in the dielectric material, then deposit anon-lattice-matched semiconductor (30) such as germanium or a compoundsemiconductor in the trench. The threading dislocations (40), shown asdotted lines, propagate upward, typically at approximately a 45 degreeangle from the interface, then intersect the sidewalls of the trench,where they terminate. Threading dislocations (40) do not propagate downthe length of the trench because they propagate in a directionperpendicular to the faceted growth face of the crystal—the facets guidethe dislocations to the sidewalls, where the dislocations terminate. Werefer to the region in the trench where the sidewalls trap threadingdislocations as the “trapping region” (50). The upper region of thenon-lattice-matched semiconductor (30), above the trapping region (50),is a relatively defect-free region (60).

ART addresses the issue of cracking caused from mismatch of thermalexpansion coefficients for these reasons: (1) the stresses are smallbecause the epitaxial layers are thin; (2) the material can elasticallyaccommodate the stresses arising from thermal expansion mismatch becausedimensions of the ART openings are small; and (3) the SiO2 pedestals,which are more compliant than the semiconductor materials, may deform toaccommodate the stress.

Continuous high-quality films of high-quality III-V semiconductors orother non-lattice-matched materials may be provided on silicon wafersusing Aspect Ratio Trapping as shown in FIG. 2. This technique issimilar to the technique illustrated in FIG. 1, except that we continueto grow the non-lattice-matched semiconductor until the growth frontsfrom adjacent trenches coalesce to form a single continuous film (70).Additional defects, which we call “coalescence defects” (80), form atsome of the “coalescence regions” where the growth fronts meet. However,the defect density is much lower than the defect density of anon-lattice-matched semiconductor grown directly on a silicon wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates the principle of Aspect Ratio Trapping, a method ofdepositing high-quality compound semiconductors or othernon-lattice-matched semiconductors on silicon wafers;

FIG. 2 illustrates the technique for growing continuous films ofhigh-quality compound semiconductors or other non-lattice-matchedsemiconductors on silicon wafers by Aspect Ratio Trapping;

FIG. 3 shows the generic structure of semiconductor diodes;

FIG. 4 shows a semiconductor diode according to a first embodiment;

FIGS. 5 and 6 show exemplary successive stages of construction for thefirst embodiment semiconductor diode;

FIG. 7 is a flowchart illustrating a method of fabrication according tothe first embodiment;

FIGS. 8, 9, and 10 illustrate variations on the method illustrated inFIG. 7;

FIG. 11 shows a donor wafer according to a second embodiment;

FIG. 12 is a flow chart illustrating a method of creating a secondembodiment donor wafer;

FIGS. 13 and 14 show variations on the method illustrated in FIG. 12;

FIGS. 15 through 17 illustrate various steps in the method of exploitinga donor wafer to create a gallium nitride substrate;

FIG. 18 is a flow chart illustrating the method illustrated in FIGS. 15through 17;

FIGS. 19 and 20 show variations on method illustrated in FIG. 18;

FIG. 21 shows how cracks can appear in an epitaxially grown film;

FIG. 22 illustrates a method of reducing the thermally induced stressesin a coalesced film of semiconductor material grown on a siliconsubstrate by Aspect Ratio Trapping;

FIG. 23 is a flow chart illustrating the method shown in FIG. 22;

FIG. 23A illustrates exemplary intermediate results from an LEDfabrication process;

FIG. 23B shows an exemplary diode structure for another embodiment of anLED;

FIG. 24 through 28 illustrate steps in constructing a single chipcontaining a plurality of diode devices according to a third embodiment;

FIG. 29 shows a structure manufactured according to the thirdembodiment; and

FIG. 30 is a flow chart illustrating a method of creating a structureaccording to the third embodiment.

DETAILED DESCRIPTION

Embodiments of the disclosure provide novel and useful architectures forsemiconductor diodes made using coalesced films of compoundsemiconductors or other non-lattice-matched semiconductors deposited onsilicon wafers by Aspect Ratio Trapping. The semiconductor diode is thefundamental building block of solar cells, light-emitting diodes,resonant tunneling diodes, semiconductor lasers, and other devices.

Aspects of the present disclosure include a reduction in the costs ofsolar cells, light-emitting diodes, and other compound semiconductordevices by creating them on high-quality, large-area, low-cost siliconwafers instead of smaller, more expensive substrates.

Other aspects of embodiments of the present disclosure provide forremoval of the silicon wafer substrate from a semiconductor diode fordevices in which the substrate can degrade performance, such as alight-emitting diode.

Still other aspects of embodiments of the present disclosure provide aneconomical way to fabricate a gallium nitride substrate; e.g., ahigh-quality film of gallium nitride on a thermally matched substratesuch as polycrystalline aluminum nitride.

Other aspects of embodiments of the present disclosure provide lessexpensive donor wafers for creating gallium nitride films, which canthen be transferred to other substrates such as aluminum nitridesubstrates.

Another aspect of the present disclosure is to mitigate thermallyinduced cracking in coalesced films grown by Aspect Ratio Trapping.

Yet other aspects of embodiments of the present disclosure provide moreeconomical ways to create single chips containing a plurality of diodedevices made from different semiconductor materials.

In the following description, exemplary diode structures are generallydiscussed in the context of a single diode; semiconductor engineers andothers skilled in the art will understand that most applications requiremultiple diodes, typically integrated onto a single chip.

In general, semiconductor diodes disclosed in this document have thegeneric structure illustrated in FIG. 3: a substrate (101), a bottomdiode region (102), an active diode region (103), a top diode region(104), an electrical contact on the top of the device (105), and anelectrical contact on the bottom of the device (106). Each of the dioderegions (102, 103, 104) may be comprised of multiple layers.

The bottom diode region (102) and the top diode region (104) haveopposite doping types. For example, if the bottom diode region (102) ispredominantly n-type doped (with an electron donor such phosphorous,arsenic, or antimony), then the top diode region (104) will bepredominantly p-type doped (with an electron acceptor such as boron oraluminum), and vice versa. Heavy doping in both the bottom diode region(102) and the top diode region (104) provides a low-resistance pathwayfor current to enter and leave the device. Typical doping levels of thetop and bottom regions would be in the range of 1017-1020 cm-3. Typicaldoping levels of the active region would be below 1017 cm-3. Note thatthe use of “top” and “bottom” for designating regions is a matter ofconvenience and in some frames of reference a top region can be locatedabove a bottom region. For example, consider a diode formed above asubstrate with its top region formed above its bottom region. If thediode is flip-chip bonded to a handle wafer and then the substrate isremoved, the frame of reference for viewing the diode typically isflipped. In this case the top region will be viewed as being below thebottom region.

The substrate (101) is typically a silicon wafer, although in differentembodiments a variety of other substrates including sapphire and siliconcarbide, are suitable. At least some portion of the substrate (101)usually will have the same predominant doping type (either n or p) asthe bottom diode region (102) to facilitate good electrical contactbetween the bottom diode region (102) and the substrate (101).

The detailed structure of the active diode region (103) may depend uponnumerous factors, including the intended application. In one form, theactive diode region (103) is formed by the junction of the top dioderegion (102) and the bottom diode region (104). In this case, it can bedesirable to vary the doping of the top and bottom regions near thejunction. In an LED, the active diode region (103) may contain manylayers that include both doped layers and thin undoped quantum wellswhere electrons and holes can recombine and generate photons. In anotherexample of a solar cell, the active diode region (103) may consist of asingle layer of moderately n-doped or moderately p-doped semiconductormaterial to absorb incident photons and generate an electron-hole pair.

The materials used to form the diode regions are well known to those ofskill in the art. Typical examples of useful semiconductor materialsare: Group IV materials, such as Si, C, or Ge, or alloys of these suchas SiC or SiGe; Group II-VI compounds (including binary, ternary, andquaternary forms), e.g., compounds formed from Group II materials suchas Zn, Mg, Be or Cd and Group VI materials such as Te, Se or S, such asZnSe, ZnSTe, or ZnMgSTe; and Group III V compounds (including binary,ternary, and quaternary forms), e.g., compounds formed from Group IIImaterials such as In, Al, or Ga and group V materials such as As, P, Sbor N, such as InP, GaAs, GaN, InAlAs, AlGaN, InAlGaAs, etc. Those ofskill in the art understand how to select and process these materialsbased on desired properties such as bandgaps, lattice constants, dopinglevels, etc.

FIG. 4 shows an illustrative semiconductor diode embodiment. This diodearchitecture is suitable for devices in which the substrate can degradeperformance. In a light-emitting diode, for example, a silicon substratecan absorb light generated within the device. In the embodimentillustrated in FIG. 4, we have removed the silicon substrate.

FIG. 5 shows the results of the preliminary stages of construction. Thefoundation is a substrate (1000) such as a silicon wafer in which thesurface preferably has a (111) crystal orientation, although otherorientations are possible and in some embodiments other orientationssuch as (100) can be selected. The substrate (1000) can be eithern-doped or p-doped, depending on the configuration of the diode-baseddevice. The first step is to deposit a layer of dielectric material(1010) such as SiO2 or SiNx onto the silicon wafer (1000) by chemicalvapor deposition (CVD) or another deposition technique. In devices wherereflection of light from the dielectric layer creates a problem, siliconnitride can be preferable because its index of refraction is closer tothat of common semiconductor materials. The thickness of the dielectricfilm is typically 200 to 400 nm, but it can be thicker or thinner.

Then we pattern openings for aspect ratio trapping, such as trenches(1020) with substantially vertical sidewalls in the layer of dielectricmaterial (1010), thereby exposing the surface of the silicon wafer(1000) within the trenches. Two exemplary ways to pattern a trench(1020) are by conventional photolithography or by reactive ion etchtechniques. As would be recognized by one skilled in the art based onthe disclosure herein, the trench could be another shaped opening suchas a hole, recess or ring for example. The width of the trench (1020)should be equal to or less than the thickness of the dielectricmaterial. This condition emerges from the principles of Aspect RatioTrapping: the ratio of the height of the trench (1020) to the width ofthe trench (1020) should generally be greater than or equal to 1 inorder to trap threading dislocations. Further details regarding thistechnique are disclosed in co-pending and commonly assigned U.S. patentapplication Ser. No. 11/436,198, and U.S. patent application Ser. No.11/852,078, which are hereby incorporated in their entirety byreference). And in (Park et al., Appl. Phys. Lett. 90, 052113 [2007]),which is incorporated herein by reference.

In some cases, it may be advantageous to clean the surface of thesilicon substrate (1000) at the bottom of the trenches (1020) to preparefor epitaxial growth of the bottom diode region. For one version of asuitable cleaning process, which includes an oxygen plasma etch, seePark et al., Appl. Phys. Lett. 90, 052113 [2007].

FIG. 6 illustrates the results of the next several steps. First we growthe bottom diode region (1030). The semiconductor material for thebottom diode region (1030) depends on the device. For a solar cell, thebottom diode region (1030) is, for example, indium gallium phosphide(InGaP). For a light-emitting diode, the bottom diode region (1030) is,for example, gallium nitride (GaN). We can also make the bottom dioderegion from many other semiconductor materials, including compoundsemiconductor materials, which have useful properties for devices suchas lasers and resonant tunneling diodes. Exemplary semiconductormaterials are described above.

It is possible to dope the bottom diode region (1030) in situ duringepitaxial growth or to dope it ex situ by ion implantation. (As ageneral matter, it is generally preferable to dope the bottom dioderegions, active diode regions, and top diode regions mentioned in thisdisclosure, and it is possible to dope them either in situ duringepitaxial growth or ex situ by ion implantation.)

We refer to a portion of the bottom diode region (1030) in the trenches(1020) as the “trapping region” (1050) because it traps dislocationssuch as threading dislocations (1040), which originate at the interfacebetween the bottom diode region (1030) and the substrate (1000) andpropagate upward towards the side walls. FIG. 6 illustrates thethreading dislocations (1040) as dashed lines. The portion of the bottomdiode region (1030) which lies above the trapping region (1050) remainsrelatively free of defects. This low-defect region enables us to createhigh-quality compound semiconductor devices on high-quality, large-area,low-cost silicon wafers. For some materials, such as GaN, InN, AlN, orternary or quarternary combinations of these, a dislocation density ofe.g. less than or equal to 108/cm2 is low enough to be useful for deviceapplications. For some other materials, such as GaAs and InP, a somewhatlower dislocation density is typically required to be useful fordevices, e.g. less than or equal to 106/cm2.

We continue to grow the bottom diode region (1030) until a) the materialoverflows the trenches, and b) the material from adjacent trenchescoalesce to form a single continuous film. It is typically desirable toplanarize the bottom diode region (1030) by chemical mechanicalprocessing or any other suitable technique before further fabrication.The next steps are to deposit the active diode region (1060) and the topdiode region (1070). In most embodiments, the active diode region (1060)and the top diode region (1070) have the same or approximately the samelattice constants as the bottom diode region (1030).

FIG. 4 shows the results of the final steps. We bond a handle substrate(1080) to the top diode region (1070). In some embodiments, it may bepreferable to planarize the top diode region (1070) in order to achievea high-quality bond to the handle substrate (1080). In still otherembodiments, it may be preferable to include an intermediate layerbetween the top diode region (1070) and the handle substrate (1080) toimprove adhesion, minimize thermal mismatch, or the like. The handlesubstrate (1080) could be part of an LED packaging fixture. Bondingmethods are well known, including those used in flip-chip bonding, wherethe top portion of an LED is bonded to a surface that is part of an LEDpackage. The handle substrate (1080) may be conductive, or it maycontain conductive elements which serve as contacts for the top dioderegion (1070). Then we remove the silicon substrate (1000) by standardtechniques such as grinding, chemical etch-back, laser ablation, or somecombination of those methods.

Finally, we add a first electrical contact (1090) to the bottom dioderegion (1030) and a second electrical contact (1100) to the handlesubstrate (1080). In various embodiments the material for the electricalcontacts can be, for example, a strip of conductive metal such ascopper, silver, or aluminum, or a layer of relatively transparentconductive oxide such as indium tin oxide. For light-emitting diodes,the bottom electrical contact (1100) should preferably be a highlyreflective conductive material, such as silver, which will reflect theinternally created light so it will exit the LED from another surface.

People skilled in the art of semiconductor diode manufacturing know manymaterials for and ways of adding electrical contacts. FIG. 4 shows oneoption for creating the first electrical contact (1090): we have removedthe dielectric layer (1010) to expose the surface of the bottom dioderegion (1030). Here, the dielectric material (1010) is removed bystandard techniques such as etching. In an LED, the trapping regions(1050) shown in FIG. 4 could effectively roughen the surface to reduceinternal reflection of light, provided that their size and spacing werecorrect.

The following are examples of process parameters sufficient to form thebottom, active, and top diode regions according to embodiments in thisdisclosure. First, a substrate and a patterned dielectric layer as knownin the art are provided. Exemplary process parameters for bottom,active, and top diode regions, for of a GaAs and AlGaAs-based LED,according to one embodiment are below.

A) Bottom diode region (e.g., 1030): (e.g., 100 nm-500 nm thick layer ofGaAs);

Pressure: 0.1 atm

Precursors: TMG (Trimethylgallium) and 20% AsH3 (Arsine), diluted in H2

Temperature: 720 C

N-type: dope with siliconB) Active diode region (e.g., 1060): AlGaAs layer for carrierconfinement (15 nm thick)

Pressure: 0.1 atm

Precursors: TMG, TMA (Trimethylaluminium), and 20% arsine, diluted in H2

Temperature: 850 C

N-type: dope with siliconGaAs Quantum well for emission (10 nm thick)

Pressure: 0.1 atm

Precursors: TMG and 20% arsine, diluted in H2

Temperature: 720 C

No dopingAlGaAs layer for carrier confinement (15 nm thick)

Pressure: 0.1 atm

Precursors: TMG, TMA (Trimethylaluminium), and 20% arsine, diluted in H2

Temperature: 850 C

P-type: dope with zincC) Top diode region (e.g., 1070): (e.g., 100 nm-500 nm thick layer ofGaAs)

Pressure: 0.1 atm

Precursors: TMG and 20% arsine, diluted in H2

Temperature: 720 C

P-type: dope with zinc

Exemplary prophetic process parameters of growth conditions (e.g., CVD)for bottom, active, and top diode regions, for a GaN and InGaN-basedLED, according to the first embodiment 1 are below.

A) Bottom diode region (e.g., 1030):GaN low-temperature buffer (e.g., 30 nm thick)

Pressure: 100 Torr

Precursors: TMG and NH3, diluted in H2

Temperature: 530 C

N-type: dope with siliconGaN hi-temperature buffer (e.g., 500 nm thick)

Pressure: 100 Torr

Precursors: TMG and NH3, diluted in H2

Temperature: 1030 C

N-type: dope with siliconB) Active diode region (e.g., 1060):InGaN Quantum well layer for emission (e.g., 2 nm thick)

Pressure: 100 Torr

Precursors: TMG+TMI+NH3, diluted in N2

Temperature: 740 C

No dopingGaN barrier layer for carrier confinement (e.g., 15 nm thick)

Pressure: 100 Torr

Precursors: TMG and NH3, diluted in H2

Temperature: 860 C

N-type: dope with siliconC) Top diode region (e.g., 1070): GaN p-contact layer (e.g., 100 nmthick)

Pressure: 100 Torr

Precursors: TMG and NH3, diluted in H2

Temperature: 950 C

P-type: dope with magnesium

Embodiment No. 1, shown in FIG. 4, includes a semiconductor diode madefrom compound semiconductors or other lattice-mismatched materials on asilicon wafer comprising these elements: a bottom diode region (1030),an active diode region (1060), a top diode region (1070), a handlesubstrate (1080), a first electrical contact (1090), a second electricalcontact (1100), and a trapping region (1050) where threadingdislocations terminate.

The bottom diode region (1030), the active diode region (1060), and thetop diode region (1070) will have low defect densities (typically lessthan or equal to 5×107 per square centimeter) as a result of growing thebottom diode region (1030) as a coalesced film by Aspect Ratio Trapping.

Turning now to FIG. 7, which illustrates a method of fabricating adevice according to the first embodiment. The method includes:depositing a layer of dielectric material (1010) onto the surface of asilicon wafer (1000), patterning trenches (1020) in the layer ofdielectric material (1010) to expose the surface of the silicon wafer(1000), each trench (1020) having substantially vertical sidewalls, andthe ratio of the height to the width of each trench (1020) being greaterthan or equal to 1, growing a semiconductor material to form a bottomdiode region (1030) which fills the trenches (1020) and coalesces toform a single continuous film, growing a semiconductor material upon thebottom diode region (1030) to form an active diode region (1060),growing a semiconductor material upon the active diode region (1060) toform a top diode region (1070), bonding a handle substrate (1080) to thetop diode region (1070), removing the silicon substrate (1000), removingthe dielectric material (1010), fabricating a first electrical contact(1090) on the surface of the bottom diode region (1030), and fabricatinga second electrical contact (1100) on the surface of the handlesubstrate (1080).

FIG. 8 summarizes a variation of the method illustrated in FIG. 7 inwhich we clean the surface of the silicon wafer at the bottom of thetrenches before depositing the bottom diode region. FIG. 9 summarizesanother variation in which we planarize the surface of the bottom dioderegion before growing the active diode region. FIG. 10 summarizes yetanother variation in which we planarize the surface of the top dioderegion before bonding it to the handle substrate.

Another exemplary embodiment allows coalesced films deposited by AspectRatio Trapping to create gallium nitride substrates. In this document,as in the LED industry, the term “gallium nitride substrate” means athin film as well known in the art of gallium nitride (GaN) grown onto,or bonded onto, a substrate made from a material other than GaN. LEDmanufacturers typically buy GaN substrates from materials suppliers,then deposit additional layers of GaN and other materials to createLEDs. A typical GaN substrate consists of a layer of GaN deposited on awafer of sapphire (Al2O3) silicon carbide. The worldwide market forgallium nitride substrates currently is about $300 million per year.

Materials suppliers typically deposit GaN onto Al2O3 because these twomaterials have a reasonably good lattice match. However, GaN and Al2O3have very different thermal expansion coefficients. When LEDmanufacturers heat the GaN/Al2O3 structure to deposit additional layers,the difference in thermal expansion coefficients causes the structure tobow. The bowing causes some portion of the Al2O3 wafer to lose contactwith the susceptor, the substrate heater in the deposition chamber. As aresult, the temperature of the Al2O3 wafer varies as a function ofposition. The inconsistent Al2O3 wafer temperature causes variations inlayer composition and layer thickness. The practical consequence is thatmanufacturers have difficulty controlling the emission wavelength of theresulting LED.

An emerging technique for creating GaN substrates may solve or at leastameliorate this problem. The essence of this emerging technique is toextract a GaN thin film from a donor wafer and to bond that film to asubstrate of aluminum nitride, which has a thermal expansion coefficientsimilar to that of GaN. The donor wafer is typically a wafer ofsingle-crystal GaN. The conventional method of extracting the GaN thinfilm from the donor wafer involves ion implantation and exfoliation. Themanufacturers implant hydrogen ions into the donor wafer to create acleave plane, then split the donor wafer by annealing it or by applyingmechanical pressure. This technique makes it possible to extractmultiple thin films from a single donor wafer.

FIG. 11 illustrates a second embodiment that provides for a novel donorwafer which can be produced at lower cost than a donor wafer ofsingle-crystal GaN. We begin with a substrate (1000) such as a siliconwafer in which the surface has a (111) crystal orientation. However,other orientations are possible and in some embodiments otherorientations such as (100) can be selected. The substrate (1000) can beeither n-doped or p-doped. Onto that substrate (1000), we deposit alayer of dielectric material (1010). Next, we pattern trenches withsubstantially vertical sidewalls in the layer of dielectric material(1010), thereby exposing the surface of the silicon wafer (1000). In thestage of manufacture illustrated in FIG. 11, the trenches have beenfilled with semiconductor material (1100) as described below. As before,to promote trapping of threading dislocations, the width of each trenchshould be less than or equal to the thickness of the dielectricmaterial. Optionally, we might then clean the surface of the siliconsubstrate (1000) at the bottom of the trenches by the techniquesdescribed above.

The next step is to grow a layer of semiconductor material (such as GaN)(1110) until the material overflows the trenches and the material fromadjacent trenches coalesce to form a single continuous film. Exemplarysemiconductor materials are described above. The portion of thesemiconductor material (1110) which fills the trenches serves as atrapping region (1050); it traps the threading dislocations (1040). Theportion of the semiconductor material (1110) above the trapping regions(1050) grows substantially free of threading dislocations. Coalescencedefects may appear at some of the locations where the growth fronts fromadjacent trenches merge, but the density of coalescence defects is lowenough (generally less than or equal to 5×107/cm2) to allow thestructure to be technologically useful.

FIG. 11 illustrates a novel donor wafer which can yield multiple thinfilms from the layer of semiconductor material (1110). For example, theillustrated embodiment could provide a source of multiple GaN filmswhich could be separated by ion implantation and exfoliation, thenbonded to aluminum nitride wafers. Aspect Ratio Trapping makes itpossible to create high-quality GaN films for this donor wafer on aninexpensive silicon substrate.

The embodiment shown in FIG. 11, is a donor wafer composed of theseelements: a silicon wafer substrate (1000), a layer of dielectricmaterial (1010) covering the silicon wafer substrate (1000), the layerof dielectric material (1010) containing trenches which expose thesurface of the silicon wafer substrate (1000), the trenches havingsubstantially vertical sidewalls, and the ratio of the height to thewidth of the trenches being greater than or equal to 1, a layer ofsemiconductor material (1110) which fills the trenches and overflows thetrenches to create a single continuous film, and trapping regions (1050)within the trenches wherein threading dislocations (1040) intersect thesidewalls of the dielectric material and terminate.

FIG. 12 summarizes a method to fabricate the donor wafer shown in FIG.11. It includes these steps: depositing a layer of dielectric material(1010) onto the surface of a silicon wafer (1000), patterning trenchesin the layer of dielectric material (1010) to expose the surface of thesilicon wafer (1000), each trench having substantially verticalsidewalls, and the ratio of the height to the width of each trench beinggreater than or equal to 1, and growing a layer of semiconductormaterial (1110) such as GaN which fills the trenches and coalesces toform a single continuous film.

FIG. 13 summarizes a variation on the method illustrated in FIG. 12, inwhich we clean the surface of the silicon wafer substrate (1000) at thebottom of the trenches before growing the semiconductor material (1110).FIG. 14 summarizes another variation in which we planarize the surfaceof the semiconductor material (1110).

Described next is a way of exploiting the donor wafer concept describedabove to create a GaN substrate, such as a high-quality GaN film bondedto an AlN wafer. More generally, it is a method of creating a layer ofsemiconductor material bonded to an arbitrary substrate material.

After we create the donor wafer (shown in FIG. 11), FIG. 15 illustratesa next step: we implant the layer of semiconductor material (1110) withions, such as, for example, hydrogen ions or a combination of hydrogenand helium ions, to create a cleave plane (1120). Next we bond the layerof semiconductor material (1110) by conventional techniques to a handlesubstrate (1130), as shown in FIG. 16. If the semiconductor material(1110) is GaN, a generally preferred material for the handle substrate(1130) is a material with a similar thermal expansion coefficient, suchas AlN.

The final step is to split the layer of semiconductor material (1110) atthe cleave plane (1120) by annealing it or by applying mechanicalpressure. The result is shown in FIG. 17: a layer of semiconductormaterial (1110) bonded to a handle substrate (1130). This structure isespecially useful when the defect density of the semiconductor material(1110) is low (e.g., less than or equal to 5×107/cm2), when there is amismatch of lattice constants between the semiconductor material (1110)and the handle substrate (1130), and/or there is a close match ofthermal expansion coefficients between the semiconductor material (1110)and the handle substrate (1130). Again, for some materials, such as GaN,InN, AlN, or ternary or quarternary combinations of these, a dislocationdensity of e.g. less than or equal to 108/cm2 is low enough to be usefulfor device applications. For some other materials, such as GaAs and InP,a somewhat lower dislocation density is typically required to be usefulfor devices, e.g. less than or equal to 106/cm2.

FIG. 18 summarizes the above described method to create a structurecomposed of a layer of semiconductor material bonded to a substratecomprising these steps: depositing a layer of dielectric material (1010)onto the surface of a silicon wafer (1000), patterning trenches in thelayer of dielectric material (1010) to expose the surface of the siliconwafer (1000), each trench having substantially vertical sidewalls, andthe ratio of the height to the width of each trench being greater thanor equal to 1, growing a layer of semiconductor material (1110) whichfills the trenches and coalesces to form a single continuous film,implanting the layer of semiconductor material (1110) with ions tocreate a cleave plane (1120), bonding a handle substrate (1130) to thelayer of semiconductor material (1110), and splitting the layer ofsemiconductor of material (1110) at the cleave plane (1120).

FIG. 19 summarizes a variation of the method illustrated in FIG. 19, inwhich we clean the surface of the silicon wafer (1000) at the bottom ofthe trenches before depositing the layer of semiconductor material(1010). FIG. 20 summarizes another variation of Method C in which weplanarize the surface of the layer of semiconductor material (1110)before implanting it with ions.

In some embodiments, coalesced films grown by Aspect Ratio Trapping maybe susceptible to cracking because the epitaxial materials typicallyhave larger thermal expansion coefficients than the silicon wafersubstrate. When the structure cools from the growth temperature, thefilm contracts more than the substrate. As FIG. 21 illustrates, tensilestrain in the film can lead to cracks (1140). Cracks (1140) can impairthe performance and the reliability of devices such as LEDs or solarcells.

FIG. 22 shows a novel solution: create divots (1150) in the layer ofsemiconductor material. It would be possible to create these divots bystandard techniques, such as lithography, etching, or laser ablation.The divots (1150) effectively limit the area of the coalesced film. As aresult, they reduce the thermally induced stresses in the semiconductormaterial. If the divots have the proper size and spacing, they willallow the semiconductor material to accommodate the thermal stresselastically, without cracking. If the divots have the proper size andspacing, they will allow the semiconductor material to accommodate andlargely reduce or eliminate wafer bow. FIG. 23 summarizes this method ofreducing the thermally induced stresses in a coalesced film ofsemiconductor material grown on a silicon substrate by Aspect RatioTrapping: depositing a layer of dielectric material (1010) onto thesurface of a silicon wafer (1000), patterning trenches in the layer ofdielectric material (1010) to expose the surface of the silicon wafer(1000), each trench having substantially vertical sidewalls, and theratio of the height to the width of each trench being greater than orequal to 1, growing a layer of semiconductor material (1030) which fillsthe trenches and coalesces to form a single continuous film, andcreating divots (1150) in the semiconductor material.

In one embodiment, exemplary first divots can extend along a firstdirection in parallel with a regular, irregular, prescribed, periodic orintermittent spacing, for example, between 0.1 um and 1.0 um. In thismanner, the semiconductor material can be made into a plurality ofstrips or segments. Exemplary second divots similar to the first divotscan extend in a second direction (e.g., perpendicular) to the firstdirection. In this manner, the semiconductor material can be made into aplurality of islands. If the first and second divot pattering wasregular and equal, the resulting islands would be squares, however,other known shapes for such islands may be used. In one embodiment, thesemiconductor material can include a lower diode region, an active dioderegion and an upper diode region.

An exemplary method of reducing the thermally induced stresses incoalesced films forming an LED grown on a silicon substrate by AspectRatio Trapping (ART) can include: depositing a layer of dielectricmaterial (1010) onto the surface of a silicon wafer (1000), patterningtrenches or holes in the layer of dielectric material (1010) to exposethe surface of the silicon wafer (1000) with unpatterned lanes orsections between areas filled with patterned trenches or holes, eachtrench having substantially vertical sidewalls, and the ratio of theheight to the width of each trench or hole being sufficient to create atrapping region, and successively growing a coalesced bottom dioderegion, an active diode region and a top diode region corresponding tothe patterned areas within the lanes of unpatterned dielectric material(1010) by standard methods (e.g., MOCVD) to result in divots over thelanes of unpatterned dielectric material (1010).

FIG. 23A illustrates exemplary results from these several steps.Separating (e.g., saw or cleave) individual LEDs corresponding to thedivots in the semiconductor material and/or additional steps previouslydescribed with respect to the above described first embodiment canresult in an alternative embodiment of a LED.

In one embodiment, divots in each lane can occupy 10-30% of a length orwidth dimension of a corresponding LED. Exemplary divots can includeslanted sidewalls at a 45 degree angle to a top surface of an adjacentLED. Alternatively, sidewalls of divots can use a greater or smallerangle such as 30 degrees, 60 degrees, etc.

The active regions for LEDs in a III-N system can be grown over relaxedGaN. For example, such relaxed GaN can be c-plane bulk GaN wafer orsubstantially relaxed c-plane GaN epilayer grown over a substrate ofsapphire or silicon carbide. However, for visible light emission, theemission region must contain a significant fraction of indium. Thus, theemission regions for visible light LEDs in a III-N system have one ormore InGaN alloy layers. InGaN has a larger lattice constant than GaN.To avoid or reduce dislocations that accompany relaxation of strainedepilayers, such InGaN films remain strained over the underlying GaNlayer (e.g., as they are grown to have substantially the same latticeconstant as the underlying GaN layer). Further, the c-plane III-Nsemiconductor materials are polar materials and the strain in theemission region leads to significant polarization fields (e.g.,piezoelectric polarization), which can be deleterious to deviceperformance. For example, device/emission efficiency can be degraded orthe wavelength of emission can be shifted.

FIG. 23B shows an exemplary diode structure for another embodiment of anLED. In FIG. 23B, at least a portion of a lower diode region close tothe substrate comprises InGaN (instead of GaN). The InGaN lower dioderegion can be a relaxed layer with reduced or controlled defectdensities formed using ART techniques. Such an InGaN lower diode regioncan be a platform for emission regions (e.g., LED emission regions) withsignificantly reduced strain. For example, further growth of subsequentlayers for the active diode region (e.g., InGaN with low or no strain)and upper diode region result in emission regions with significantlyreduced strain. As shown in FIG. 23B, a lower diode region is relaxedN-type InGaN over and partially in a defect trapping region, an activediode region is subsequent layers of AlGaN barrier region (e.g., latticespacing equal to the lower diode region), a reduced strain InGaNemission region and an AlGaN barrier region (e.g., lattice spacing equalto the emission region) In FIG. 23B, the substrate can be a siliconsubstrate, and contacts to the upper/top and lower/bottom diode regionscan be subsequently added (e.g., as described above).

Manufacturers of LEDs have created multi-chip solutions in which theymounted semiconductor chips made of different materials into a singlepackage or module. This technique allows them to combine differentcolors to achieve white light.

Researchers developing high-efficiency solar cells have createdmulti-chip solutions in which they mounted semiconductor chips made ofdifferent materials into a single package or module. They wereimplementing a “split spectrum” approach in which they directed aportion of the solar spectrum onto a chip optimized for that portion ofthe spectrum.

In both of these cases, the costs of mounting and packaging multiplechips may be prohibitively high. We propose a single-chip solution,which has the potential to be much less expensive. For illustrativepurposes, we will describe a single chip with three separate diodes.

FIG. 24 shows the first few steps. We deposit a layer of a firstdielectric material (1010) onto a silicon substrate (1000). Then wepattern trenches (1160) with substantially vertical sidewalls in a firstregion of the layer of dielectric material (1010). Each trench exposesthe surface of the silicon wafer (1000). The width of each trench shouldbe equal to or less than the thickness of the dielectric material sothat the trench can trap threading dislocations.

Optionally, we might then clean the surface of the silicon substrate(1000) at the bottom of the trenches (1160) by the techniques describedabove.

The next step is to mask the top surface of the structure in alllocations except the location of diode device number 1 (1195). We thengrow the bottom diode region (1170), a layer of semiconductor materialwhich fills the trenches and coalesces to form a single continuous film,as shown in FIG. 25. Exemplary semiconductor materials are describedabove. Misfit dislocations form at the interface between the bottomdiode region (1170) and the silicon substrate (1000). Threadingdislocations propagate upward at a 45 degree angle, intersect thesidewalls of the trenches, and terminate within a trapping region.

At this point, it might be useful to planarize the bottom diode region(1170).

Then we grow a layer of semiconductor material to form the active dioderegion (1180) and yet another layer of semiconductor material to formthe top diode region (1190). Together, the bottom diode region (1170),the active diode region (1180), and the top diode region (1190) make updiode device number 1 (1195).

Next we deposit a layer of a second dielectric material (1200). Forexample, if the first dielectric material was SiO2, the seconddielectric material might be SiNx. We selectively remove the seconddielectric material (1200) by wet or dry etch from all regions exceptthe region which contains diode device number 1, leaving the structureshown in FIG. 26.

Then we mask the structure in all locations except the location of diodedevice number 2 (1240). In the next steps, we create diode device number2, following the same steps by which we created diode device number 1,thereby yielding the structure shown in FIG. 27. As shown in the FIG.27, a bottom diode region (1210), an active diode region (1220), and atop diode region (1230) make up diode device number 2 (1240).

We deposit another layer of the second dielectric material (1200) tocover diode device number 2 (1240). Then we selectively remove thislayer of the second dielectric material (1200) by wet or dry etch fromthe region which will contain diode device number 3 (1280).

Next we mask the structure in all locations except the location of diodedevice number 3 (1280) and create diode device number 3 (1280),following the same steps by which we created diode device number 1(1195) and diode device number 2 (1240). The result is the structureshown in FIG. 28. As shown in the FIG. 28, a bottom diode region (1250),an active diode region (1260), and a top diode region (1270) make updiode device number 3 (1280).

Finally, we cover diode device number 3 (1280) with the seconddielectric material (1200), pattern contact vias through the seconddielectric material (1200), and deposit individual contacts (1290) onthe top of each diode device. We also create a bottom electrical contact(1300) preferably but not necessarily common to all devices on thesupport substrate (1000).

The result is shown in FIG. 29. The various diode devices can containdifferent sets of semiconductor materials for the top, active, andbottom diode regions. In each diode device, the bandgaps of thematerials are tailored to emit light of the desired color (in an LED) orto absorb light of the desired frequency (in a solar cell). Thisembodiment represents a relatively inexpensive way to create multiplediode devices on a single chip.

In summary, a single chip containing a plurality of diode devices,comprising the following elements: a silicon wafer substrate (1000), alayer of a first dielectric material (1010) covering the silicon wafersubstrate (1000), this layer of first dielectric material (1010)containing trenches (1160) which expose the surface of the silicon wafersubstrate (1000), these trenches (1160) having substantially verticalsidewalls, and the ratio of the height to the width of these trenches(1160) being greater than or equal to 1, a plurality of diode devices(at least three devices 1995, 1240, 1280), each of which comprises alayer of semiconductor material which fills trenches (1160) in oneportion of the layer of first dielectric material (1010) and overflowsthe trenches (1160) to create a bottom diode region (1170, 210, 1250), atrapping region for trapping threading dislocations within the trenches(1160), an active diode region (1180, 1220, 1260), and a top dioderegion (1190, 1230, 1270), a layer of a second dielectric material(1200) covering the diode devices (1995, 1240, 1280), top electricalcontacts (1290), and a bottom electrical contact (1300).

FIG. 30 summarizes a method of fabricating the structure shown in FIG.29. This method of fabricating a plurality of diode devices on a singlechip includes these steps:

-   -   depositing a layer of a first dielectric material (1010) onto        the surface of a silicon wafer (1000),    -   patterning trenches (1160) in the layer of first dielectric        material (1010) to expose the surface of the silicon wafer        (1000), each trench (1160) having substantially vertical        sidewalls, and the ratio of the height to the width of each        trench (1160) being greater than or equal to 1,    -   masking the structure in all locations except the location of        diode device No. 1 (1195),    -   taking these steps to create diode device No. 1: growing a layer        of semiconductor material which fills the trenches, overflows        the trenches, and coalesces to create a bottom diode region        (1170) in the form of single continuous film; growing a layer of        semiconductor material to create an active diode region (1180);        and growing a layer of semiconductor material to create a top        diode region (1190),    -   depositing a layer of a second dielectric material (1200),    -   selectively removing the second dielectric material (1200) from        all regions except the region which contains diode device No. 1        (1195),    -   masking the structure in all locations except the location of        diode device No. 2 (1240),    -   creating diode device No. 2 (1240) by the same steps as diode        device No. 1 (1195),    -   depositing the second dielectric material (1200) to cover diode        device No. 2 (1240),    -   selectively removing the second dielectric material (1200) from        the region which will contain diode device No. 3 (1280),    -   masking the structure in all locations except the location of        diode device No. 3 (1280),    -   creating diode device No. 3 (1280) by the same steps as diode        device No. 1 (1195) and diode device No. 2 (1240),    -   depositing the second dielectric material (1200) to cover diode        device No. 3 (1280),    -   patterning contact vias through the second dielectric material        (1200),    -   creating top electrical contacts (1290) to diode device No. 1,        diode device No. 2, and diode device No. 3, and    -   creating a bottom electrical contact (1300) common to all three        diode devices.

It would, of course, be possible to create any number of diode deviceson a single chip, the only limitation being the amount of availablespace.

Embodiments of the application were described using trenches to providetrapping regions, however, alternative structural configurations ofrecesses with cross-sections functionally sufficient and intended totrap defects may be used herein as “trenches.”

Embodiments of the application provide methods, structures or apparatusthat may use and/or form by epitaxial growth or the like. For example,exemplary suitable epitaxial growth systems may be a single-wafer ormultiple-wafer batch reactor. Various CVD techniques may be used.Suitable CVD systems commonly used for volume epitaxy in manufacturingapplications include, for example, an Aixtron 2600 multi-wafer systemavailable from Aixtron, based in Aachen, Germany; an EPI CENTURAsingle-wafer multi-chamber systems available from Applied Materials ofSanta Clara, Calif.; or EPSILON single-wafer epitaxial reactorsavailable from ASM International based in Bilthoven, The Netherlands.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” “another embodiment,” “otherembodiments,” etc., means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. The appearances of suchphrases in various places in the specification are not necessarily allreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anyembodiment, it is submitted that it is within the purview of one skilledin the art to affect such feature, structure, or characteristic inconnection with other ones of the embodiments. Furthermore, for ease ofunderstanding, certain method procedures may have been delineated asseparate procedures; however, these separately delineated proceduresshould not be construed as necessarily order dependent in theirperformance. That is, some procedures may be able to be performed in analternative ordering, simultaneously, etc. In addition, exemplarydiagrams illustrate various methods in accordance with embodiments ofthe present disclosure. Such exemplary method embodiments are describedherein using and can be applied to corresponding apparatus embodiments,however, the method embodiments are not intended to be limited thereby.

Although few embodiments of the present invention have been illustratedand described, it would be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention. The foregoing embodiments aretherefore to be considered in all respects illustrative rather thanlimiting on the invention described herein. Scope of the invention isthus indicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein. As usedin this disclosure, the term “preferably” is non-exclusive and means“preferably, but not limited to.” Terms in the claims should be giventheir broadest interpretation consistent with the general inventiveconcept as set forth in this description. For example, the terms“coupled” and “connect” (and derivations thereof) are used to connoteboth direct and indirect connections/couplings. As another example,“having” and “including”, derivatives thereof and similar transitionalterms or phrases are used synonymously with “comprising” (i.e., all areconsidered “open ended” terms)—only the phrases “consisting of” and“consisting essentially of” should be considered as “close ended”.Claims are not intended to be interpreted under 112 sixth paragraphunless the phrase “means for” and an associated function appear in aclaim and the claim fails to recite sufficient structure to perform suchfunction.

Advantageous embodiments could include a photonic device comprising asubstrate, a dielectric material including two or more openings thatexpose a portion of the substrate, the two or more openings each havingan aspect ratio of at least 1, a bottom diode material comprising acompound semiconductor material that is lattice mismatched to thesubstrate, and wherein the compound semiconductor material occupies thetwo or more openings and is coalesced above the two or more openings toform the bottom diode region, a top diode material, and an active dioderegion between the top and bottom diode materials. The substrate couldbe selected from the group consisting of silicon, sapphire, and siliconcarbide. The substrate could be a single crystal silicon wafer. Thesingle crystal silicon wafer could have a crystal orientation of (111)or (100). The active diode region could comprise a p n junction formedby a junction of the top and bottom diode materials. The active dioderegion could comprise a material different from the top and bottom diodematerials, and could form an intrinsic region of a p-i-n junction formedbetween the top and bottom diode materials. The active diode regioncould comprise multiple quantum wells formed between the top and bottomdiode materials. The dielectric material could comprise a materialselected from the group consisting essentially of silicon dioxide,silicon nitride, silicon oxynitride, oxides of hafnium, silicates ofhafnium, oxides of zirconium, silicates of zirconium, and combinationsthereof. The opening could be a trench or could be a hole having anaspect ratio of at least 1 in two perpendicular axes. The semiconductormaterial could comprise a Group III-V compound, a Group II VI compound,or a Group IV alloy. The bottom diode material could include an n-typedopant and the top diode material could include a p-type dopant. Thedevice could further include a contact formed over the top diode region.The contact could be a transparent conductor. The device could yetfurther include a second contact formed adjacent the substrate.

Another advantageous embodiment could include a photonic device having asubstrate, and a photonic diode comprising a first region proximate atop surface of the substrate, a second region proximate the firstregion, and an active region between the first and second regions,wherein the second region includes a surface adjacent the active region,the surface being generally parallel to the substrate top surface, andthe second region includes at least one defect-trapping region spacedapart from the active region, the defect trapping region including asurface that extends away from the substrate top surface. The surface ofthe first diode region could be bonded to a handle substrate. Anintermediate layer could be bonded to the handle substrate between thefirst diode region and the handle substrate. The handle substrate couldinclude a conductor electrically connected to the first diode region.The device could further include a contact connected to the handlesubstrate and in electrical communication with the first diode region.

Another advantageous embodiment includes a method of making a photonicdevice. The method could include depositing a layer of a dielectricmaterial onto a substrate, patterning two or more openings in thedielectric material to expose portions of the surface of the substrate,the two or more openings having an aspect ratio of at least 1, forming abottom diode region by growing a compound semiconductor material that islattice mismatched to the substrate in the two or more openings andallowing the compound semiconductor material to fill in the two or moreopenings and coalesce above the two or more openings to form acontinuous layer, forming an active diode region on the bottom dioderegion, and forming a top diode region on the active diode region. Themethod could further include bonding a handle wafer to the top dioderegion and removing the substrate.

Another advantageous embodiment could provide for a photonic devicehaving a bottom diode region including two or more threading dislocationtrapping regions and comprised of a compound semiconductor material, anactive diode region, a top diode region, a handle substrate, a firstelectrical contact in communication with the handle substrate, and asecond electrical contact in communication with the bottom diode region.

Yet another advantageous embodiment could provide for a method of makinga photonic device comprising depositing a layer of a dielectric materialonto a substrate, patterning two or more openings in the dielectricmaterial to expose portions of the surface of the substrate, the two ormore openings having an aspect ratio of at least 1, forming a bottomdiode region by growing a compound semiconductor material that islattice mismatched to the substrate in the two or more openings andallowing the compound semiconductor material to fill in the two or moreopenings and coalesce above the two or more openings to form acontinuous layer, forming an active diode region on the bottom dioderegion, forming a top diode region on the active diode region, bonding ahandle wafer to the top diode region, removing the substrate, removingthe dielectric material, contacting a first electrical contact with thehandle substrate, and contacting a second electrical contact with thebottom diode region.

Still another advantageous embodiment includes a method of making astructure comprising a semiconductor material bonded to a substrate. Themethod could include depositing a layer of a dielectric material onto asubstrate, patterning two or more openings in the dielectric material toexpose portions of the surface of the substrate, the two or moreopenings having an aspect ratio of at least 1, growing a layer of acompound semiconductor material that is lattice mismatched to thesubstrate in the two or more openings and allowing the semiconductormaterial to fill in the two or more openings and coalesce above the twoor more openings to form a continuous layer, implanting ions into thesemiconductor material to create a cleavage plane, bonding a handlesubstrate to the semiconductor material, and cleaving the layer ofsemiconductor material at the cleavage plane.

In some aspect, advantageous embodiments could provide for a chipincluding a plurality of discrete photonic devices thereon. The chipcould include a substrate, a first dielectric material layer coveringthe substrate and having a plurality of openings therein having anaspect ratio of at least 1, a plurality of discrete photonic devices,each discrete photonic device comprising (i) a layer of semiconductormaterial that is mismatched to the substrate that occupies at least twoopenings and is coalesced above the occupied openings to form a singlebottom diode region, (ii) an active diode region, and (iii) a top dioderegion, a second layer of dielectric material covering the plurality ofdiscrete photonic devices, at least one top electrical contact; and atleast one bottom electrical contact.

Yet another advantageous method could provide for a method of making achip including a plurality of discrete photonic devices thereoncomprising depositing a layer of a dielectric material onto a substrate,patterning a first set of openings in the dielectric material to exposeportions of the surface of the substrate, the first set of openingshaving an aspect ratio of at least 1, forming a first bottom dioderegion by growing a layer of a semiconductor material that is latticemismatched to the substrate in the first set of openings and allowingthe semiconductor material to fill in the first set of openings andcoalesce above the first set of openings to form a continuous layer,forming a first active diode region on the first bottom diode region,forming a first top diode region on the first active diode region,growing a layer of dielectric material to cover the first bottom dioderegion, first active diode region, and first top diode region,patterning a second set of openings in the dielectric material to exposeportions of the surface of the substrate, the second set of openingshaving an aspect ratio of at least 1, forming a second bottom dioderegion by growing a layer of a semiconductor material that is latticemismatched to the substrate in the second set of openings and allowingthe semiconductor material to fill in the second set of openings andcoalesce above the second set of openings to form a continuous layer,forming a second active diode region on the second bottom diode region,forming a second top diode region on the second active diode region, andgrowing a layer of dielectric material to cover the second bottom dioderegion, second active diode region, and second top diode region. Themethod could further include contacting a first electrical contact withthe substrate, contacting a second electrical contact with first topdiode region, and contacting a third electrical contact with the secondtop diode region.

In one aspect, the present disclosure is directed to a photonic devicecomprising a substrate, a dielectric material including two or moreopenings that expose a portion of the substrate, the two or moreopenings each having an aspect ratio of at least 1, a bottom diodematerial comprising a compound semiconductor material that is latticemismatched to the substrate, and wherein the compound semiconductormaterial occupies the two or more openings and is coalesced above thetwo or more openings to form the bottom diode region, a top diodematerial, and an active diode region between the top and bottom diodematerials.

In another embodiment, the present disclosure is directed to a photonicdevice comprising a substrate and a photonic diode comprising a firstregion proximate a top surface of the substrate, a second regionproximate the first region, and an active region between the first andsecond regions, wherein the second diode region includes a surfaceadjacent the active photonic diode region, the surface being generallyparallel to the substrate top surface, and the second diode regionincludes at least one defect-trapping region spaced apart from theactive photonic diode region, the defect trapping region including asurface that extends away from the substrate top surface.

In another embodiment, the present disclosure is directed to a method ofmaking a photonic device, the method comprising depositing a layer of adielectric material onto a substrate, patterning two or more openings inthe dielectric material to expose portions of the surface of thesubstrate, the two or more openings having an aspect ratio of at least1, forming a bottom diode region by growing a compound semiconductormaterial that is lattice mismatched to the substrate in the two or moreopenings and allowing the compound semiconductor material to fill in thetwo or more openings and coalesce above the two or more openings to forma continuous layer, forming an active diode region on the bottom dioderegion, and forming a top diode region on the active diode region.

In another embodiment, the present disclosure relates to a methodcomprising epitaxially growing a first crystalline semiconductormaterial on a first substrate. The substrate comprises a secondcrystalline semiconductor material, the first crystalline semiconductormaterial being lattice mismatched to the second crystallinesemiconductor material. A portion of the first crystalline semiconductormaterial distal from the first substrate is substantially free ofthreading dislocations. The method further includes bonding the portionof the first crystalline semiconductor material to a second substrate,and after the bonding, removing the first substrate.

In another aspect, the present disclosure relates to a method comprisingforming a dielectric layer on a substrate of a first crystallinesemiconductor material, the dielectric layer having an opening exposingthe first crystalline semiconductor material. The method includesepitaxially growing a second crystalline semiconductor material in theopening and over a surface of the dielectric layer distal from thesubstrate. The second crystalline semiconductor material is latticemismatched to the first crystalline semiconductor material. Threadingdislocations arie from the lattice mismatch between the firstcrystalline semiconductor material and the second crystallinesemiconductor material terminating in the opening. A portion of thesecond crystalline semiconductor material over the surface of thedielectric layer has a dislocation density of less than or equal to10⁸/cm². The method further includes forming a divot in the secondcrystalline semiconductor material to the surface of the dielectriclayer.

In yet another aspect, the present disclosure relates to a methodcomprising forming a first crystalline semiconductor material on a firstsubstrate, the first crystalline semiconductor material having a firstportion distal from the first substrate, the first portion of the firstcrystalline semiconductor material having a dislocation density of lessthan or equal to 10⁸/cm², the first portion of the first crystallinesemiconductor material comprising a first diode region. The methodincludes forming an active diode region on the first diode region, andforming a second diode region on the active diode region. The methodfurther includes bonding a second substrate to the second diode region,and forming a first contact on the first crystalline semiconductormaterial, the first crystalline semiconductor material being disposedbetween the first contact and the active diode region

What is claimed is:
 1. A method comprising: epitaxially growing a firstcrystalline semiconductor material on a first substrate, the substratecomprising a second crystalline semiconductor material, the firstcrystalline semiconductor material being lattice mismatched to thesecond crystalline semiconductor material, a portion of the firstcrystalline semiconductor material distal from the first substrate beingsubstantially free of threading dislocations; bonding the portion of thefirst crystalline semiconductor material to a second substrate; andafter the bonding, removing the first substrate.
 2. The method of claim1, wherein the first crystalline semiconductor material is a III-Nmaterial, the second crystalline semiconductor material is silicon, andthe second substrate is aluminum nitride.
 3. The method of claim 1further comprising implanting the first crystalline semiconductormaterial with ions to form a cleave plane, wherein the removing thefirst substrate comprises splitting the first crystalline semiconductormaterial at the cleave plane.
 4. The method of claim 1 furthercomprising: forming an active diode region on the portion of the firstcrystalline semiconductor material after the removing the firstsubstrate, the portion of the first crystalline semiconductor comprisinga bottom diode region; and forming a top diode region on the activediode region.
 5. The method of claim 1 further comprising forming adielectric layer on the first substrate, the dielectric layer having anopening to the first substrate, the first crystalline semiconductormaterial being epitaxially grown in the opening and on a surface of thedielectric layer distal from the first substrate, threading dislocationsarising from the lattice mismatch between the first crystallinesemiconductor material and the second crystalline semiconductor materialterminating in the opening.
 6. The method of claim 5, wherein theopening has substantially vertical sidewalls, a ratio of a height of theopening to a width of the opening being greater than or equal to
 1. 7.The method of claim 1, wherein a thermal expansion coefficient of thesecond substrate matches a thermal expansion coefficient of the firstcrystalline semiconductor material.
 8. A method comprising: forming adielectric layer on a substrate, the substrate comprising a firstcrystalline semiconductor material, the dielectric layer having anopening exposing the first crystalline semiconductor material;epitaxially growing a second crystalline semiconductor material in theopening and over a surface of the dielectric layer distal from thesubstrate, the second crystalline semiconductor material being latticemismatched to the first crystalline semiconductor material, threadingdislocations arising from the lattice mismatch between the firstcrystalline semiconductor material and the second crystallinesemiconductor material terminating in the opening, a portion of thesecond crystalline semiconductor material over the surface of thedielectric layer having a dislocation density of less than or equal to10⁸/cm²; and forming a divot in the second crystalline semiconductormaterial to the surface of the dielectric layer.
 9. The method of claim8 further comprising: forming an active diode region on the secondcrystalline semiconductor material, the second crystalline semiconductorcomprising a bottom diode region; and forming a top diode region on theactive diode region.
 10. The method of claim 8, wherein the opening hassubstantially vertical sidewalls, a ratio of a height of the opening toa width of the opening being greater than or equal to
 1. 11. The methodof claim 8, wherein the dielectric layer has a first plurality ofopenings and a second plurality of openings, the first plurality ofopenings being in a first region of the dielectric layer, the secondplurality of openings being in a second region of the dielectric layer,the second crystalline semiconductor material being epitaxially grown inthe first plurality of openings and the second plurality of openings, anun-patterned lane of the dielectric layer being between the first regionand the second region, the divot being over and to the surface of thedielectric layer in the un-patterned lane.
 12. The method of claim 8,wherein the forming the divot comprises using etching and/or laserablation.
 13. The method of claim 8, wherein the divot laterallysurrounds a region of the first crystalline semiconductor material. 14.A method comprising: forming a first crystalline semiconductor materialon a first substrate, the first crystalline semiconductor materialhaving a first portion distal from the first substrate, the firstportion of the first crystalline semiconductor material having adislocation density of less than or equal to 10⁸/cm², the first portionof the first crystalline semiconductor material comprising a first dioderegion; forming an active diode region on the first diode region;forming a second diode region on the active diode region; bonding asecond substrate to the second diode region; and forming a first contacton the first crystalline semiconductor material, the first crystallinesemiconductor material being disposed between the first contact and theactive diode region.
 15. The method of claim 14 further comprisingremoving the first substrate after the bonding the second substrate tothe second diode region.
 16. The method of claim 14 further comprisingforming a dielectric layer on the first substrate, the dielectric layerhaving openings to the substrate, second portions of the firstcrystalline semiconductor material being formed in the openings, thefirst substrate comprising a second crystalline semiconductor materialthat is lattice mismatched to the first crystalline semiconductormaterial, the second portions of the first crystalline semiconductormaterial being formed in the respective openings, threading dislocationsarising from the lattice mismatch between the first crystallinesemiconductor material and the second crystalline semiconductor materialterminating in the respective opening.
 17. The method of claim 14further comprising forming a dielectric layer on the first substrate,the dielectric layer having openings to the substrate, second portionsof the first crystalline semiconductor material being formed in theopenings, the first substrate comprising a second crystallinesemiconductor material that is lattice mismatched to the firstcrystalline semiconductor material, the second portions of the firstcrystalline semiconductor material being formed in the respectiveopenings, the first portion of the first crystalline semiconductormaterial forming a continuous layer on the dielectric layer.
 18. Themethod of claim 14 further comprising forming a dielectric layer on thefirst substrate, the dielectric layer having openings to the substrate,second portions of the first crystalline semiconductor material beingformed in the openings, the first substrate comprising a secondcrystalline semiconductor material that is lattice mismatched to thefirst crystalline semiconductor material, the second portions of thefirst crystalline semiconductor material being formed in the respectiveopenings, each of the openings having a width and a height, a ratio ofthe height to the width being greater than or equal to
 1. 19. The methodof claim 14 further comprising forming a second contact on the secondsubstrate, the second substrate being disposed between the secondcontact and the second diode region.
 20. The method of claim 14, whereinthe first contact is further formed on second portions of the firstcrystalline semiconductor material, the second portions comprisingdislocations, the dislocations terminating at respective sidewalls ofthe second portions of the first crystalline semiconductor material.